It is known to produce stannous chloride from stannic chloride in a divided cell (divided by an asbestos diaphragm) by introducing a warm stannic chloride solution into the anode compartment of the cell and withdrawing stannous chloride solution from the cathode compartment of the cell. See, for example, U.S. Pat. No. 1,597,653. As disclosed therein, chlorine is evolved at the anode, electrolysis is conducted at temperatures of 70.degree. C. or higher and a portion of the stannic chloride must be retained to prevent deposition of metallic tin.
Electrolytic cells using a porous diaphragm, e.g., an asbestos type diaphragm, permit the flow of electrolyte solution from one electrode compartment to another which flow may cause contamination. In addition, such cells must contend also with the plating of the metal on the cathode which is undesirable from the standpoint of process efficiencies.
In contrast to known fluid permeable membranes, ion permselective membranes, also referred to as ion exchange membranes, have been found useful in a variety of fluid purification applications. One specific use is the demineralization of water. Other specific uses include the treatment of picking liquors to produce sulfuric acid and electrolytic iron, the treatment of copper or leaching solutions to produce hydrochloric acid and copper and the purification of aluminum sulfate solutions by electrolytically depositing iron therefrom. See, Industrial & Engineering Chemistry, Vol. 54, No. 6, page 29 (June 1962) and U.S. Pat. Nos. 3,537,961 and 3,347,761. In addition, cationic permselective membranes have been disclosed for use in processes to produce stannic oxide sol products (see U.S. Pat. No. 3,723,273), anionic permselective membranes have been disclosed for use in a process to form tin and lead salts, e.g., stannous sulfate (see U.S. Pat. No. 3,795,595) and cationic permselective membranes have been suggested for use in the regeneration and recycling of chromium etching solutions. See Chemical Engineering, June 4, 1979, page 77.
Stannous chloride in more recent years has been conventionally prepared by dissolving metallic tin in aqueous hydrochloric acid and evaporating the solution until crystals of the dihydrate SnCl.sub.2.2H.sub.2 O, commonly known as tin salt, separate. The anhydrous salt can also be made by heating metallic tin in a stream of gaseous hydrogen chloride or by reacting tin metal with chlorine gas in the presence of liquid stannic chloride.
A particularly effective method for preparing stannous chloride is disclosed in U.S. Pat. No. 3,816,602 in which about 1 mol of tin metal, about 1 mol of fuming or essentially anhydrous stannic chloride and at least 4 mols of free water are reacted to produce stannous chloride.
One of the problems with presently available processes for producing stannous chloride is the requirement for the addition of tin metal to reduce the stannic chloride to the stannous chloride form. As tin prices increase, the utilization of such processes results in an increasing cost of the stannous chloride. In addition, the tin metal may contain various metallic impurities (for example, copper, iron, arsenic, antimony or lead) which may deleteriously affect the final product and prevent its utilization in certain end use products and applications. For example, the use of stannous chloride in connection with food additives requires very low tolerences of copper and arsenic. These metal impurities also pose problems in electrotinplating applications.